The heterobimetallic complex [Cu(II)Mn(III)(L)2(py)4](ClO4)·EtOH (1) built using the pro-ligand 2,2′-biphenol (LH2), contains a rare example of a Jahn–Teller compressed Mn(III) centre. Dc magnetic susceptibility measurements on 1 reveal a strong antiferromagnetic exchange between the Cu(II) and Mn(III) ions mediated through the phenolate O-atoms (J = −33.4 cm−1), with magnetisation measurements at low temperatures and high fields suggesting significant anisotropy. Simulations of high-field and high frequency powder EPR data suggest a single-ion anisotropy DMn(III) = +4.45 cm−1. DFT calculations also yield an antiferromagnetic exchange for 1, though the magnitude is overestimated (JDFT = −71 cm−1). Calculations reveal that the antiferromagnetic interaction essentially stems from the Mn(dx2−y2)–Cu(dx2−y2) interaction. The computed single-ion anisotropy and cluster anisotropy also correlates well with experiment. A larger cluster anisotropy for the S = 3/2 state compared to the single-ion anisotropy of Mn(III) is rationalised on the basis of orbital mixing and various contributions that arise due to the spin–orbit interaction.